The present invention relates generally to a ceramic composite electrolytic device, and, more specifically, to a device and methods for manufacturing a ceramic composite electrolytic device for use in the generation of electrical power and heat.
In the past, stationary, vehicular and portable ceramic composite electrolytic devices such as fuel cells for generating electric power and heat or for generating oxygen, have been difficult to manufacture for numerous reasons. First, numerous prior art devices used ceramic to ceramic type fabrication techniques which resulted in a product which was not sufficiently tough to be reliable during transport or usage. The ceramic-to-ceramic interface was brittle and would tend to crack readily. Additionally, fabrication costs for such units were high due to the use of expensive ceramic materials, together with complicated manufacturing methods. The high temperature at which such devices must operate limited the choice of materials for use in the devices. Where metals were used, high operating temperatures tended to weaken the metals as well as increase their corrosion and oxidation rates. As a result, expensive ceramic materials were used. Such materials have had difficulties including cracking and failure of the seals. These difficulties are made worse in the event of shock, vibration and thermal cycling to high operating temperatures. Fabrication techniques may also have included expensive permanent or hermetic gas seals, which were often unsuccessful. Prior art units also tend to be too large to meet desired space and weight requirements. Moreover, such devices were unable to meet desired power requirements despite such additional disadvantages. For example, in the case of a stack of small cells having continuous output requirements for use in a micro-vehicle, minimal output such as a few Watts are desired. In a larger vehicle, manned or unmanned, power outputs are generally desired to be in the range of 1-100 kWatts. For large vehicles or stationary power supplies, for example for utility power, megawatt requirements may be desired. Devices of this type would preferably have relatively small physical dimensions.
Additional disadvantages with prior art techniques are set forth in the background of U.S. Pat. No. 5,069,987 concerning electrical power generation, which is incorporated herein by reference. Still further enhancements continue to be made to the mechanical properties of ceramic cell technology as discussed in U.S. Pat. No. 5,624,542. However, such improvements continue to have disadvantages, including the use of large amounts of expensive precious metals such as silver and palladium. Also, the use of increased amounts of metal in the composite result in undesirable direct electrical connections, which limit the usefulness of the cell in certain applications.
According to the present invention, a ceramic composite electrolytic device is provided which may be used for generation of electric power or heat. In the power generation system or device of the present application, a reliable, mechanically rugged device is provided. In particular, such device may be stationary, vehicular and/or portable, and is capable of delivering electrical power at a desired wattage, which in various embodiments may be from a few watts to a kilo or mega watt output. In the fuel cell device embodiment of the present application, an efficient, economical, relatively light weight, reliable, mechanically rugged device, which has reduced pollutant emissions is provided. Such devices are advantageously used in the production of electrical power at any required location where electric power conversion from fuel is needed, generation of power for electrically powered vehicles, or generation of electric power from methane produced by land fills, as a few examples, or in military aircraft or life support systems, for example in small unmanned aerial vehicles for use in military surveillance. Additionally, such electrical generators may be used as the power source for an oxygen generator device.
The present device is a solid-state electrochemical source of electrical power which is maintenance free. The present device has a preferred fluid fuel embodiment and a solid fuel embodiment. In the pre-loaded solid fuel embodiment the use of fuel tanks, pumps, lines and fuel processing is eliminated, which significantly reduces difficulties with volume and weight constraints.
When the system is heated to its comparatively lower operating temperature of between 500xc2x0 C. and 1200xc2x0 C., the device spontaneously produces power making use of the transportability of ions, such as oxide ions (Oxe2x88x922), or hydroxide ions (OHxe2x88x92), across an electrolytic ductile ceramic barrier. According, to Faraday""s law, amperage is proportional to the number of electrons transferred per carbon (C) atom multiplied by Faraday""s constant (approximately 96,500). (A=(#exe2x88x92/Catom)(F)(gmoles C/second). Thus, for the production of carbon monoxide (CO) from carbon the number of electrons transferred is 2, and for carbon dioxide (CO2) From carbon the number is 4. As a result, amperage of the cell equals (2)(96,500)(gmoles C/second) for CO production from carbon. Thus, the rate of fuel consumption may be controlled by electronic control of the amperage through the device. It is noted that each gram-mole of carbon weights 12.0 grams. At a nominal current of 27 amps, each cell in the device will electrochemically consume about 100 mg of carbon per minute, if the carbon is converted to carbon monoxide. If carbon dioxide is produced, only about 50 mg C/min. is consumed.
Further advantages are obtained with the present device since the embodiments are less costly to manufacture, due to their substantial use of common, inexpensive stainless steels. The use of such metals enables the use of metal-to-metal welds for the high temperature seals and other connections. Also, the use of flexible solid electrolytes within cells of the device increases its life, due to the relative ductile, flexible, fracture tough, solid ceramic and metal composite materials.